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81, 64 Byte Error Correction Code

IP.com Disclosure Number: IPCOM000084065D
Original Publication Date: 1975-Sep-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 89K

Publishing Venue

IBM

Related People

Price, DW: AUTHOR

Abstract

In a storage system designed with semiconductor chips, each containing 9 output bits, as for example 256 x 9, 512 x 9, etc. arrays, the probability of multibit failures due to failure of a single chip is relatively high. In such a system it is desirable to correct all multibit failures occurring within one chip.

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81, 64 Byte Error Correction Code

In a storage system designed with semiconductor chips, each containing 9 output bits, as for example 256 x 9, 512 x 9, etc. arrays, the probability of multibit failures due to failure of a single chip is relatively high. In such a system it is desirable to correct all multibit failures occurring within one chip.

The (81,64) code illustrated as an H-Matrix in the figure, yields a unique error indication (syndrome) for all bit failures within any single (9 bit) byte, with the exception of the case where all 9 bits in any byte are in error. The syndrome for that failure is identical for each of the 9 bytes; thus, it is detectable, but not correctable.

The code consists of 64 data bits and 17 check bits. The 64 data bits comprise 9 bits each in byte -0 to byte -6 with the remaining data bit contained in byte -7. Byte -7 also contains the check bits C0 through C7; byte -8 contains check bits K0 through K8.

C0 is the exclusive OR (odd parity) of all bit -0 bits in byte -0 through byte -8; C1 is the exclusive OR of all bit -1 bits, and so forth through C7.

The K bits are related to the bits in the byte in a rotational manner, e.g., K0 is the exclusive OR of byte -0 bit -2, byte -1 bit -4, byte -2 bit -6, etc. In this fashion, a unique byte failure indication is available for any single-byte failure (1 to 8 bits) by the relationship existing between the C and the K syndrome bits.

The equation for these byte failure indications are as fol...